Jo McCarroll investigates the science behind storing your crops

When you grow your own fruit and veges, you often talk (possibly rather smugly) about how much better everything tastes when it’s picked “fresh from the garden”. I have done it myself in the pages of this very magazine, rhapsodising about the pleasures of sun-warmed tomatoes eaten straight off the vine, and the incredible sweetness of corn when it’s picked and cooked straight away.

Well, it turns out that the idea that the fresher the food is the better it tastes – and indeed the better it is for you – is, at best, a half truth. I was reading a new book from British botanist and garden writer James Wong,

How to Eat Better, in which he explains that the phytonutrients (which are the chemical produced by plants, some of which have beneficial effects on our health when we eat them) in some fruit and vegetables increase after a period of storage. Since phytonutrients also include the compounds that give fresh food flavour, as well as health benefits, that means some fresh foods actually become both better tasting and better for you if detached from the plant for a spell before it is served.

Take tomatoes. Tomatoes, as we have written in NZ Gardener many times before, contain a phytonutrient known as lycopene which is thought to have a long list of health benefits, including helping prevent some cancers. James refers to research by Japanese and Indonesian scientists which found that lycopene levels almost doubled in a tomato stored at room temperature for one week after it was picked (but interestingly storing tomatoes in the fridge reduced the amount of lycopene they contained, as well as causing them to lose their flavour).

Mushrooms, he says, if left on a sunny windowsill for an hour or two after they are picked, will contain more vitamin D than if they are eaten straight away (fun fact: that’s because the skin of mushrooms reacts to the sun much like our own skin does). Likewise the skin of apples (at least if they are stored in the sun rather than in the fridge) will continue to react to the UV rays when off the tree, increasing the vitamin C and antioxidising, disease-fighting polyphenols which that fruit contains. The heart-healthy compounds in strawberries will continue to increase for four days after being picked if they are stored at room temperature (but again, not if you keep them in the fridge), while the level of sugar in pumpkins and winter squash continues to increase for a month or so after they are picked – and that doesn’t just mean it is sweeter to eat, but that sugar fuels the creation of antioxidising carotenes.

But then there are some crops that are better for you the fresher they are. Broccoli, for instance, contains a group of sulphur-based chemicals known as glucosinolates, consumption of which is purported to reduce risk of heart disease and protect against some cancers. James refers to a study in Spain which attempted to replicate the conditions a head of broccoli might have endured if you purchased it at a supermarket – keeping it first for a week in a chiller (to mimic the time being stored and transported), then for a couple of days at room temperature (to replicate the period spent on the shop shelves). That caused the level of glucosinolates in this cruciferous crop to fall by up to 80 per cent. A study published in the scientific journal Food Chemistry found that six days after it was picked broccoli had lost up to 70 per cent of its vitamin C and up to 50 per cent of its antioxidant activity. So that’s one crop it’s definitely worth growing yourself and eating fresh… and luckily now is a great time to plant some more!

Have a great May in the garden everyone. Jo McCarroll